This invention relates to compositions of the type comprising a film-forming component and an amino compound, wherein the composition cures by reaction between the amino compound and hydroxyl functionality present on the film forming material. More particularly, the invention relates to thermosetting compositions of the aforementioned type wherein the composition includes a latent reactive catalyst for the hydroxyl/amino curing reaction. Still more particularly, the invention relates to thermosetting compositions of the aforementioned type wherein the film forming component bearing hydroxyl functionality is generated by the heat induced breakdown of the latent reactive catalyst.
Thermosetting compositions which cure by reaction of hydroxyl functionality with an amino compound are well known in the art. It is also well recognized in the art that it is desirable to catalyze the hydroxyl/amino crosslinking reaction in order to obtain a quicker and more complete cure of the composition, particularly when the composition is to be used as a coating material. To this end, catalysts for this reaction have developed and are also well known. Exemplary of the numerous known catalysts are p- toluene sulfonic acid and various organophosphate esters such as those taught by U.S. Pat. Nos. 3,960,979 and 4,018,848 to Khanna. In many compositions these catalysts also function as reactive catalysts.
While these known catalysts and reactive catalysts effectively catalyze the hydroxyl/amino reaction, they have several deficiencies. When necessary amounts of prior art catalysts are included in compositions curing via the hydroxyl/amino reaction, the compositions often lack shelf stability resulting in premature crosslinking. Many prior art catalysts have a detrimental effect on pigments, thus resulting in color changes, in some of the known catalysts cause coagulation of the compositions. Still further, some of the known catalysts result in gassing when used in compositions including metallic pigments.
The compositions of this invention employ a latent reactive catalyst which generates the catalyst in situ and, thus, do not suffer from the aforementioned deficiencies. Because the catalyst is generated in situ during cure, sufficient amounts of latent reactive catalyst may be included in the composition in order to allow for rapid cure, without causing deleterious effects, including loss of shelf life.
The compositions of the invention have particular utility as fast curing, high solids, thermosetting coating compositions. More particularly, the compositions are adapted to provide an automotive topcoat demonstrating hardness, high gloss, outstanding durability and excellent resistance to solvents and water. The compositions are particularly suitable as high solids thermosetting coating compositions adapted to be used as automotive topcoats including metallic flake as a pigment.
Because of increasingly strict solvent emission regulations in recent years, low solvent emission paints have become very desirable. A number of high solids compositions have been proposed to meet these low solvent emission requirements. However, many of these compositions are deficient because of difficulty in application, slow curing rates, lack of flexibility, poor durability and low solvent and water resistance. Many of the proposed compositions have been particularly deficient as automotive topcoats, particularly when the topcoat is to include metallic flake as pigment.
The deficiency in compositions including metallic flake results from excessive gassing as well as undesired reorientation of metallic flake during application and cure of the coating. Flake reorientation results primarily because of the very low viscosity resins used in the paint compositions to accommodate high solids. The low viscosity is not sufficient to immobilize the flakes which tend to redistribute themselves to show "reverse flop' and nonuniform distribution.
The compositions of this invention combine the above desired properties and low application viscosity with rapid cure so as to overcome deficiencies of previously proposed high solids materials and thereby achieve a high solids coating composition particularly adapted for automotive topcoates including metallic flake as pigment.